1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a liquid crystal display device in which a light loss of the liquid crystal display device is reduced in a transmission mode and a bi-directional display is provided.
2. Description of the Related Art
In these days, electronic display devices become more important for communicating and processing various information. Also, various types of electronic display devices are widely used in different industrial fields.
Generally, an electronic display device visually provides a variety of information to a user. In other words, an electrical information signal output from electronic devices is converted into a visible optical information signal in an electronic display device. Such an electronic display device serves as an interfacing means between a user and the electronic devices.
Meanwhile, owing to developments in the semiconductor technology, recent electronic devices are generally driven by lower voltage and lower power, and have a slimmer size and a lighter weight. With such a trend, a flat panel type display device which is slimmer and lighter and requires lower driving voltage and power becomes in more demand and desirable.
An LCD device among the various types of flat panel display devices is much slimmer and lighter than any other display devices, and has a lower driving voltage and lower power consumption, and also has the displaying quality similar to that of CRT-type display devices. Therefore, LCD devices are widely used in various electronic equipments.
Recently, an LCD device for performing a bi-directional image display has been developed.
Specifically, a conventional LCD device for performing the bi-directional image display includes a backlight, a first LCD panel and a second LCD panel. The first LCD panel is disposed above (or below) the backlight, and the second LCD panel is disposed below (or above) the backlight.
In the conventional LCD device for performing the bi-directional image display, light radiated from a lamp(s) is divided into two groups of light. A first group of light is provided to the first LCD panel, and a second group of light is provided to the second LCD panel. The conventional LCD device only has the function of dividing the light radiated from the lamp(s), but does not have the function of regulating an amount of each of the two groups. It is thus desired that an LCD device can divide the light radiated from the lamp(s) into two groups and also can regulate the amount of each of the two groups.
An LCD panel, which is available for the LCD device capable of performing the bi-directional image display, may have a structure in which the LCD panel can display images in a transmission mode or a reflection mode according to an amount of external light. The LCD panel includes a first substrate, a second substrate, a liquid crystal layer interposed between the first and second substrates, and pixel electrodes. The pixel electrodes are formed on the first substrate, and each of the pixel electrodes has a transparent electrode region and a reflective electrode region. Light is transmitted through the transparent electrode region in the transmission mode, and is reflected by the reflective electrode region in the reflection mode. Accordingly, the LCD panel displays images by means of the transparent electrode region in the transmission mode, and displays images by means of the reflective electrode region in the reflection mode.
The conventional LCD device having the above structure has at least the following problems.
First, since a display area of the LCD device is divided into a transmission area used in the transmission mode and a reflection area used in the reflection mode, it is not effective in aspect of utilization of the display area.
Second, since the conventional LCD device has to employ the wide band xc2xc wavelength phase difference plates covering an overall frequency band of the visible ray, as well as a first and a second polarizing plates attached on each of the first and second substrates, a manufacturing cost is elevated compared with a transmission type LCD device that displays images by means of a backlight disposed under the LCD panel.
Third, since the polarization characteristic in the transmission mode causes a light loss of 50%, there are drawbacks in that a light transmissivity decreases by 50% and a contrast ratio (C/R) is lowered.
Fourth, since xcex94nd (xcex94n: a value for representing optical anisotropy or refractive anisotropy; d: cell gap) of a liquid crystal layer is only 0.24 xcexcm which is a half of xcex94nd (0.48 xcexcm) of the conventional transmission type LCD device, the cell gap of the liquid crystal cell should be decreased to a level of 3 xcexcm, and the xcex94n of the liquid crystal also should be decreased. Accordingly, there are problems in that the manufacturing process becomes difficult and degeneration in the reliability of the liquid crystal is caused.
Accordingly, the present invention is to solve the aforementioned and other problems of the conventional art, and it is an object of the present invention to provide an LCD device capable of simplifying a structure of an LCD panel, decreasing light loss in the transmission mode and performing a bi-directional image display.
In one aspect, there is provided a liquid crystal display device comprising: a first display unit including a first liquid crystal display panel having a first substrate, a second substrate and a first liquid crystal layer between the first and second substrates, and a transflective film disposed under the first liquid crystal display panel, the transflective film having a plurality of layers in which a first layer and a second layer having different refractivity indexes from each other are alternately stacked, so that the transflective film partially reflects and partially transmits incident light incident onto the transflective film; a second display unit including a second liquid crystal display panel having a third substrate, a fourth substrate and a second liquid crystal layer between the third and fourth substrates; and a light supplying unit disposed between the first and second display units, the light supplying unit generating a first light to provide the first display unit with a first part of the first light and the second display unit with a second part of the first light, and the light supplying unit controlling an amount of the first and second parts of the first light to regulate a contrast ratio of a luminance between the first and second display units.
According to another aspect of the invention, there is provided a liquid crystal display device comprising: a first display unit including a first liquid crystal display panel having a first substrate, a second substrate and a first liquid crystal layer disposed between the first and second substrates, and a first transflective film disposed under the first liquid crystal display panel, the first transflective film having a plurality of layers in which a first layer and a second layer having different refractivity indexes from each other are alternately stacked, so that the first transflective film partially reflects and partially transmits a first incident light incident onto the first transflective film; a second display unit including a second liquid crystal display panel having a third substrate, a fourth substrate and a second liquid crystal layer disposed between the third and fourth substrates; and a light supplying unit disposed between the first and second display units, the light supplying unit dividing a first light, which is a first part of a light generated from an light source, into a third light and a fourth light to provide the first and second display units with the third and fourth light, respectively, and dividing a second light, which is a second part of the light generated from the light source, into a fifth light and a sixth light to provide the first and second display units with the fifth and sixth light, respectively, the light supplying unit controlling an amount of the third, fourth, fifth and sixth light to regulate a contrast ratio of a luminance between the first and second display units.
In an exemplary embodiment, the LCD device includes a first transflective film disposed at one of the first and second display units. The first transflective film has a plurality of layers in which a first layer and a second layer having different refractivity indexes from each other are alternately stacked, so that the first transflective film partially reflects and partially transmits a first incident light incident on the first transflective film. The LCD device includes a light supplying unit disposed between the first and second display units. The light supplying unit controls an amount of the light that is provided to the first and second display units, to thereby regulate a contrast ratio of a luminance between the first and second display units. Therefore, the structure of an LCD panel for performing a bi-directional image display can be simplified, and the light loss in the transmission mode can be reduced.
In another exemplary embodiment, the LCD device includes an anisotropy transflective film or an isotropy transflective film disposed at one of the first and second display units. The anisotropy transflective film has an optical characteristic in which light components in a specific direction are strongly reflected and polarization components in a direction perpendicular to the specific direction are partially transmitted and reflected depending on polarized state and direction of the incident light incident thereto. The isotropy transflective film has an optical characteristic in which light components are partially transmitted and reflected independent of polarized state and direction of the incident light. As a result, by a light restoring process occurring between the transflective film and the backlight, the restored light is transmitted through the transflective film repeatedly, so that transmissivity and light efficiency can be enhanced.
Further, the LCD device has no reflection electrode within liquid crystal (LC) cell and has no xc2xc-wavelength phase difference plate on each of the first substrate and the second substrate. Accordingly, compared with a conventional LCD device, the LCD device of the present invention can be made in more simple structure, and degeneration in the reliability of the liquid crystal can be prevented.
Furthermore, since the light supplying unit disposed between the first and second display units regulates the luminance of the light generated from the lamp to provide the first and second display units with the light of which luminance is regulated, the LCD device of the present invention satisfies the demand from users.